FIELD OF THE INVENTION
The invention relates to a method for testing the functional capability of a catalytic converter of an internal combustion engine with an oxygen sensor which is disposed in a catalytic converter or in an exhaust pipe downstream of the catalytic converter, the oxygen sensor having a layer which has little or no catalytic effect on the exhaust gas.
Published International Patent Application WO 93/03358, corresponding to U.S. application Ser. No. 07/741,881, filed Aug. 7, 1991, has already disclosed a method for testing a catalytic converter with an oxygen sensor. In that case, a first oxygen sensor having high catalytic activity, and a second oxygen sensor having low catalytic activity, are disposed downstream of the catalytic converter. In order to assess the functional capability of the catalytic converter, shifts in output signals of the first and second oxygen sensors in relation to an exhaust-gas ratio of air to fuel are compared with one another. The oxygen sensors are based on oxygen-conducting zirconium oxide (ZrO.sub.2). The evaluation method which is used is relatively elaborate.